Cationic polymers are used as flocculating agents, chemicals for papers, and the like. Of those, a cationic polymer having a high aqueous solution viscosity is used as a flocculating agent, especially as a flocculating agent for organic sludge.
A copolymer having a unit represented by the following formula (5) is obtained by contacting a copolymer having a unit represented by the following formula (6) with an acid as described in, for example, JP-B-42-9653 (The term "JP-B" as used herein means an "examined Japanese patent publication). However, Brookfield viscosity of the aqueous solution thereof is low and, therefore, when the copolymer is used as a cationic high molecular weight flocculating agent, the flocculating performance thereof is not sufficient. ##STR2##
wherein R.sup.1, R.sup.2 and R.sup.3 each independently represent a hydrogen atom, an aliphatic group, aralkyl group or aromatic group, each group of which may have a functional group; R.sup.4 represents a hydrogen atom or methyl group; and X represents an anion.
It is known that the copolymer having the unit represented by the above-described formula (5) is obtained by a reaction of a copolymer containing (meth)acrylonitrile with a polyamine using sulfur as a catalyst. Such conventional methods include a method using an excess amount of a polyamine (as described in, for example, JP-B-42-6271 and 42-9653); a method wherein a copolymer containing (meth)acrylonitrile is dispersed in a non-solvent therefor to react as described in, for example, JP-B-42-6271, and JP-A-58-96604, 61-83205, 61-83206, 61-83207 and 62-34905 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"); and a method wherein a reaction is conducted in a mixed state of a copolymer containing (meth)acrylonitrile and a polyamine-insoluble solid filler as described in, for example, JP-A-61-285202.
These methods, however, use sulfur as the catalyst, so that extremely toxic hydrogen sulfide is produced as a by-product during reaction. The generated hydrogen sulfide forms a salt with the product. Therefore, it was not easy to eliminate the hydrogen sulfide in the product.
The products obtained according to these methods had the problems that they formed a mass during the reaction or they became partially insoluble in water.
Conventionally, when the copolymer having the unit represented by the above-described formula (5) was used as a flocculating agent, the Brookfield viscosity of the aqueous solution thereof was low and, therefore, it was not sufficient as a flocculating agent. Further, the production method of the copolymer also had the problems that hydrogen sulfide was formed as a by-product, the product became a solid mass during the reaction, and the product became partially insoluble in water. Thus, the above-described copolymer was industrially insufficient.
Accordingly, a copolymer having the unit represented by the above-described formula (5) and also having a high Brookfield viscosity as an aqueous solution thereof as well as a method for producing the same have been desired to be developed. Thus, the object of the present invention is to provide a copolymer having the unit represented by the above-described general formula (5) and also having a high viscosity as an aqueous solution thereof, the cationic high-molecular flocculating agent comprising the same, and the process for producing the same.